1. Field of the Invention
The present invention relates to safety mechanisms for power windows in automobiles. More particularly, the present invention relates to safety mechanisms that sense obstruction in the line of movement of a power window in order to prevent injury.
2. Technical Background
A power window poses threat of injury because it can be switched ON and maintained in an ON position, regardless of obstructions caught between the window and the doorframe. The power window can be maintained in the on position either by (1) a person, a pet or a child standing or stepping on the switch, or (2) by activation of an auto-on power window. An auto-on power window includes a window having a switch that, once selected, does not require continuous activation for the window to roll up completely.
Traditionally, power windows included a mechanical safety mechanism that having either a shear pin or a clutch that stopped or disabled the window""s movement when excessive resisting force was present.
A motor-driven power window may include an electronic current-monitoring device, such that when a window is closing and reaches the gasket, the resistance met by the window as it enters the gasket causes the motor to draw more current in an attempt to provide enough torque to overcome the resistive force. The electronic current monitoring device senses an increase in the current, equivalent to an increase in required torque, and when the current exceeds a predetermined threshold, the motor stops.
By design the stopping mechanism also serves as a safety mechanism. If an object becomes lodged between the leading edge of a window and the doorframe, the window motion is resisted, the current increases, and the stopping mechanism causes the motor to stop functioning. This type of stopping mechanism uses a current reading to indicate that an obstruction is caught in the power window.
A disadvantage of this type of safety mechanism is that the current monitoring device cannot discern between the increase in current as a normal result of the resistive force as the window meets the gasket and the increase in current caused by the force of an obstructing object. In other words, either the window closes under normal conditions, or an injury or some damage occurs prior to the activation of the stopping mechanism.
There are also safety mechanisms that use contact sensors. If a window manages to push an obstruction up to the point where it is in the line of sight of a sensor embedded in the doorframe, then the sensor is designed to communicate a shut-off signal to the motor. The disadvantage of a contact sensor safety mechanism is that an obstruction may be injured or damaged.
Other sensing technology is employed in the industry, for example, Radio Frequency (RF) technologies in various frequency regimes. A sensing device can include an electrode along with a tuned oscillator circuit; both situated on or near the window. In the presence of an object near the electrode, the object couples with the circuit, changing the impedance of the tuned oscillator, and causing the frequency of the oscillator to change. The change in the frequency is detected by the system as a change in phase or a change in amplitude of the signal. When the sensing device detects a frequency change, the electronics that transmit a signal to the motor that controls the movement of the power window preventing injury or damage.
A tuned circuit approach has several disadvantages. First, a system of this type is characteristically not repeatable. The environment, including weather conditions, the number of people in a vehicle, and the impedance characteristics of the obstruction in the window affects tuned circuits. In addition, an antenna or detector can also cause shielding that interferes with signal reception.
Some power window sensing devices are infrared technology. However, infrared systems are expensive and environmentally sensitive. A passive infrared system compensates for changes in the ambient environment or background. Most passive thermal sensors are background-limited; for example, an object sensed on a bright sunny day will not have nearly the contrast as it would have in the night. Therefore, it is difficult to thermally resolve the target from its environment or from the sensor""s narcissistic radiation. Narcissistic radiation is the radiation emitted from a sensor that causes target discernment inaccuracies.
Lastly, radar or ranging type sensors can detect an obstruction in the line of movement of a power window. A ranging system uses a distributed antenna along the leading edge of the window. A transmitter coupled to one end of the antenna produces a sensor field along the antenna. A receiver at the opposite end uses a matched-filter to synchronize and identify signals unique to the matched transmitter. When an obstruction is in the line of movement of the power window, the characteristics of the signal change, indicating the presence of an object.
The present invention uses a light source in conjunction with a detector device in order to discern an obstruction between the leading edge of a power window and the top of an automobile doorframe. The light is positioned and arranged in such a way that the leading edge of the window is illuminated. Illuminating the leading edge of the power window allows the continuous detection of the movement of the leading edge window.
The present invention is designed to allow the use of various types of light sources in various configurations to create the necessary moveable illuminated leading edge of the power window to effectuate the present invention. An array of light emitting diodes (LEDs) can be placed physically inside the trailing edge of the power window, or the LEDs can be attached mechanically to the trailing edge of the power window. Either of these separate methods creates effective illumination of the leading edge of the power window detectable by sensors in sight view of the leading edge. Further, placing the light source(s) to propagate light into the trailing edge of the window permits use of the window as an optical waveguide to direct the light out the leading edge of the window. In addition, a filed fiber optic strip can be mounted to the leading edge such that the light is emitted and detectable by corresponding sensors.
The present invention uses the output of a sensor that is a result of an optically coupled source and sensor pair in order to control the movement of the power window. If the sensor detects light, then no obstruction is present between the leading edge of the power window and the detector that is mounted in the doorframe. If more than one sensor is present, a digital logical AND can be performed on all sensor outputs to ensure that none of the sensors have detected an obstruction.
Once an obstruction is detected, the output of the system can be used to prevent injury. Again, this can be accomplished in various ways. The output could be directly coupled to a device on the motor that causes the motor to either cease operating or operate in a reverse direction. Second, the indicative output of the system could be designed to interface with the controlling microprocessor of an automobile. The microprocessor could then use the obstruction indication to stop or reverse the motion of the power window.
The crux of the solution embodied in the present invention is to create a traveling transmitter or traveling emitter, so that the sensors or detectors follow the path of the window. If an obstruction breaks the traveling beam of light between the source and the detector then the movement of the window can be halted.